The present invention relates to apparatus for moving one or more knives relative to their holder, and more particularly to improvements in apparatus for automatic compensation of wear upon knives which orbit about the axis of a rotary knife holder and serve for comminution of tobacco leaves, tobacco ribs or the like. Still more particularly, the invention relates to apparatus for automatic advancement of the cutting edges of knives, especially beyond the periphery of a rotary cylindrical or polygonal holder which rotates about a fixed axis in a tobacco shredding or like machine.
It is well known to provide the knife holder in a tobacco cutting machine with means for automatically advancing the knives relative to the holder as well as with means for automatically grinding or sharpening the cutting edges of the knives when the machine is in use. Continuous or frequent advancement of the knives is desirable and normally necessary because the knives are subjected to pronounced wear, not only because a modern cutting machine turns out large quantities of shreds or otherwise configurated tobacco particles per unit of time but also because, in spite of thorough cleaning, tobacco leaves which enter a shredder still carry reasonably large quantities of sand. This contributes to rapid dulling of the cutting edges. In order to maintain the cutting edges in proper condition for satisfactory severing, the knives are normally sharpened during each revolution of their holder with attendant additional wear upon the material of the knives. Other factors which influence the wear upon the cutting edges of the knives include changeover from treatment of one type of tobacco to treatment of other tobacco types, varying quantities of sand and/or other foreign matter in the material to be comminuted, changeover from the making of relatively thin shreds to the making of larger fragments, the percentage of stem, ribs and birds' eyes in the material to be comminuted, fluctuations in the quality of tobacco in a batch which is being fed into the cutting machine and/or others. It is desirable to equip the machine with means which renders to possible to advance or feed the knives relative to their holder at a rate which is selected by full consideration of at least some of the above outlined factors to thus ensure that the quality of the comminuted material will meet the specifications of manufacturers of cigarettes or other smokers' products containing shreds or otherwise configurated particles of natural or reconstituted tobacco and/or tobacco substitutes. In accordance with the presently prevailing practice, the knives receive motion from a transmission, certain constituents of which must be replaced whenever an operator desires to change the extent to which the knives are shifted or otherwise displaced relative to their holder. This is a time-consuming operation which invariably entails prolonged interruptions of operation with attendant losses in output of the cutting machine. Such losses are especially undesirable if the cutting machine forms part of a complete production line wherein tobacco leaves are conditioned, severed and/or otherwise treated prior to introduction of comminuted tobacco into the magazine or magazines of one or more cigarette makers or the like.